The present invention relates to a method and related apparatus for measuring the adhesiveness of slow-release tablets or the like.
In particular the method of the invention relates the use of an instrument such as a dynamometer, which is known per se, but used for different types of measurements and which allows accurate and repeatable measurements to be obtained, suitable for determining the coefficient of adhesiveness of the tablets.
In the pharmaceutical sector, there are active substances that must be assimilated very slowly over time by patients, with the result that a constant, controlled release of those substances must be provided in order to guarantee full efficacy of the substances.
For this purpose, slow-release tablets have been developed to release the active substances very slowly, for example during the course of a whole night.
These tablets, in addition to containing active substances intended for xe2x80x9cslow releasexe2x80x9d, may contain also adhesive material which allows the tablets to adhere to the mucous layer of the gums.
The properties of the adhesive material are activated when hydration occurs, namely, in the case hereunder, when the tablet comes into contact with the salival liquid present in the mouth, which enables the tablet to adhere perfectly to the mucous layer of the gums.
Since these tablets should remain attached to the gums for a very long period of time, for example overnight, without the risk of becoming detached and being swallowed while a person is sleeping, the pharmaceutical technologist must solve the problem of measuring the adhesive capacity of said tablets.
To that effect, it is necessary to resort to instruments that can measure the coefficient of adhesion, i.e. the force required to raise and separate a tablet from a surface to which it has been made to adhere, in the most precise possible manner.
The use of instruments which grip the tablet and detach it from the surface, displacing it in a direction perpendicular to the surface itself, has been proposed. However, such a proposal creates various problems, for example, how to grip the tablet firmly or to repeat the measurements with constant parameters, in most cases because the tablet cannot be detached from the surface while keeping perfectly parallel to the latter, thereby giving rise to errors in the measurement recorded.
The invention aims at overcoming the abovementioned drawbacks arising during measurement of the force needed to detach the tablet from the surface to which it adheres, by acting on the tablet in a direction tangential, rather than perpendicular, to the support surface to which the tablet adheres, namely by applying to the tablet a force which is parallel to the support surface.
For this purpose a controlled force is applied to the tablet which has been made to adhere to the surface, until the tablet starts to slip, and the force required for the tablet to start to move is measured.
For this purpose, as mentioned above, the invention envisages using a dynamometer, which is currently being used to measure the hardness of tablets, but has never been used for a purpose similar to that of the invention.
Since the force needed to cause the separation and displacement of the tablet may be related to the adhesive capacity thereof, such a force may be adopted as a parameter for precise calculation of the adhesiveness.
The objects and advantages of the invention are achieved by a method for measuring the adhesiveness of slow-release tablets. According to the proposed method, the tablet is placed on the support surface, wetted with a predetermined quantity of water, and subjected to a controlled pressure for a predetermined period of time to promote adhesion. Thereafter, a plunger is allowed to act on the tablet until the latter separates from the surface to which it had been made to adhere.
The measurement of the force required to displace the tablet can therefore be related to the adhesiveness of the tablet, which can thus be precisely measured.